The present invention generally relates to an internal combustion engine, and more particularly, to a fuel supply control system in a specific operating region in which an air/fuel ratio of an air/fuel mixture is set to be different from that in the other operating region. The present invention also relates to a fuel supply control system during transfer from the specific operating region in which the air/fuel ratio of air/fuel mixture is set to be different from that in the other operating region, to such other operating region.
Conventionally, there has been widely employed a fuel supply control system arranged, e.g., to control the fuel so as to achieve a high output of the engine by decreasing an air/fuel ratio of the air/fuel mixture, i.e., by enriching the air/fuel mixture and, for example, in Japanese Laid-Open Patent Application Tokkaisho No. 59-3132, there is proposed a fuel supply control system in which a fuel increasing rate is adapted to be proportional to an opening degree of a throttle valve in a specific operating region for a smooth increase of the fuel amount at the high load period.
Incidentally, in an internal combustion engine provided with a fuel supply means for supplying fuel into an intake passage, in the case where fuel increase is started by transfer into a specific operating region, the actual air/fuel ratio is not immediately corrected to an air/fuel ratio to be set at the specific operating region, but arrives at the set air/fuel ratio only after a considerable delay.
The above phenomenon is considered to be attributable to the fact that, even if the fuel amount is increased immediately after transfer into the specific operating region, part of the increased fuel adheres to the wall surface of the intake passage, and until such adhering state reaches a certain state of equilibrium under the specific operating region, the intended amount of fuel is not actually supplied to the combustion chamber.
On the other hand, there is also invited such a problem that, in the case where the operation is transferred from the specific operating region in which the air/fuel mixture is set to be rich, to the other operating region for operation at an air/fuel mixture leaner than that, e.g., to a low load operating region, the fuel adhering to the wall surface of the intake passage in a comparatively large amount up to that time is temporarily brought into the combustion chamber following the transfer so as to enrich the air/fuel mixture conversely, and consequently, the air/fuel mixture is not readily leaned as desired, thus resulting in deterioration of the emission performance and undesirable increase of torque.